The e-mail address or addresses of the recipients. See the Send and SendAsync methods that take a recipient parameter. Also see the MailMessage.To property.

The message content. See the Send and SendAsync methods that take a body parameter. Also see the MailMessage.Body property.

To include an attachment with an e-mail message, first create the attachment by using the Attachment class, and then add it to the message by using the MailMessage.Attachments property. Depending on the e-mail reader used by the recipients and the file type of the attachment, some recipients might not be able to read the attachment. For clients that cannot display the attachment in its original form, you can specify alternate views by using the MailMessage.AlternateViews property.

You can use the application or machine configuration files to specify default host, port, and credentials values for all SmtpClient objects. For more information, see mailSettings Element (Network Settings).

To send the e-mail message and block while waiting for the e-mail to be transmitted to the SMTP server, use one of the synchronous Send methods. To allow your program's main thread to continue executing while the e-mail is transmitted, use one of the asynchronous SendAsync methods. The SendCompleted event is raised when a SendAsync operation completes. To receive this event, you must add a SendCompletedEventHandler delegate to SendCompleted. The SendCompletedEventHandler delegate must reference a callback method that handles notification of SendCompleted events. To cancel an asynchronous e-mail transmission, use the SendAsyncCancel method.

Note:

If there is an e-mail transmission in progress and you call SendAsync or Send again, you will receive an InvalidOperationException.